Instruments analyzing biological liquids are in widespread use. Thus, blood, serum, or plasma analysis instruments in more or less automated form are indispensible in hospitals and laboratories where it is of importance to know values of such blood parameters as for example pH, Pco.sub.2, Po.sub.2, hemoglobin content, electrolyte concentration etc., and parameters derived therefrom, for example "standard bicarbonate". Nowadays, it is required that these parameters be determined with great exactitude, and in some clinical situations, for example during surgery, the exact and reliable determination of blood parameters may be of decisive importance. Therefore, it is required that these instruments show a high degree of accuracy and reliability.
Blood, serum or plasma analysis instruments (below termed "blood analysis instruments" for brevity) typically operate with alternation between an analysis procedure in which a sample is introduced into the apparatus for determination of one or more parameters, and a rinse procedure in which a rinse solution is passed through the instrument manually or automatically, either introduced the same was as the sample, or, especially for automatic instruments, introduced automatically from a rinse solution reservoir connected to the instrument. The normal duration of the rinse procedure is of the same order as the normal duration of each analysis procedure. With suitable intervals, a calibration procedure takes place in which the measuring units of the instrument are calibrated against calibration liquids or gases, followed by rinsing with the rinse solution. In certain types of instruments, the calibration is performed automatically with intervals programmed into the instrument.
In practical use of blood analysis instruments, it has been found that the instruments sometimes give a certain degree of measuring errors. It may be found that the actual read-out of the instrument deviates from the data of reference standard liquids, or that the response time for one or more of the measuring units becomes abnormally long. It is presumed that such problems are primarily due to deposits on the detection areas of the measuring units, especially deposits of proteins or proteinaceous substances or lipids from the blood samples analyzed in the apparatus.